Holding apparatus for an optical element

ABSTRACT

Holding apparatus for an optical element In a holding apparatus ( 1 ) for an optical element ( 2 ) that holds the optical element during an abrasive processing of the latter, the optical element ( 2 ) is in contact with a pressure piece ( 9 ) that is adapted to a force distribution to be expected inside the optical element ( 2 ) during the processing of the optical element ( 2 ).

BACKGROUND OF TE INVENTION

1. Field of the Invention

The invention relates to a holding apparatus for an optical element according to the type defined in more detail in the preamble of claim 1. The invention also relates to a method for the abrasive processing of an optical element.

2. Description of the Related Art

Patent WO 01/54861 A1 discloses a holding chuck for optical components for the purpose of lapping and/or polishing the latter that has a cover part with a number of recesses in which the optical elements to be processed are respectively accommodated. Also located in the recesses are respective membranes to which pressure can be applied in order to press the associated optical element against the polishing tool.

A similar polishing chuck is also described in U.S. Pat. No. 2,736,993. Different versions of the chuck are described there for a concave or a convex side of the optical element to be processed.

Reference may also be made to WO 00/00324 A1 and DE 296 08 877 U1 with reference to the further prior art in the case of such holding apparatuses for optical elements.

However, it is disadvantageous in the case of all the known holding apparatuses that during the processing the optical elements are supported only inadequately and, in particular, in an undefined way such that an uncontrolled deformation of the optical element results, and this finally leads to a result of the abrasive processing that is defective with reference to accuracy to spherical shape.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a holding apparatus for an optical element with the aid of which it is possible to achieve better processing results.

According to the invention, this object is achieved by means of a holding apparatus for an optical element with the aid of a force applying device that is provided for the purpose of pressing the optical element against an abrasion tool during an abrasive processing of said optical element, the force applying device acting on a pressure piece that is in contact with the optical element and can move in the direction of the abrasion tool, the pressure piece being adapted to a force distribution that is to be expected inside the optical element during the processing of the optical element.

The holding apparatus according to the invention therefore has a pressure piece acting on the optical element and consisting of a rigid material, this adaptation to the force distribution to be expected during the processing of the optical element resulting in a controllable pressure distribution and thus in a substantially improved support of the optical element such that the latter is substantially less deformed during the processing. These lesser deformations enable better processing results, and it is possible to produce optical elements with a very much higher accuracy and/or a lesser center thickness.

Such an apparatus can have a force applying device that is provided for the purpose of pressing the optical element against the abrasion tool during the abrasive processing of said element. It is advantageous in this case when the force applying device acts on the pressure piece, which can move in the direction of the abrasion tool, since it is possible thereby to apply the force required for the abrasive processing.

In an advantageous development of the invention, it is further possible to provide that the pressure piece has on its side facing the optical element a material that prevents damage to the optical element by the pressure piece. A very gentle handling of the optical element during the holding of the latter in the holding apparatus is provided in this way. This is particularly brought about when that surface which is in contact with the pressure piece is not processed at a later point in time. Furthermore, this also results in a simple possibility of preventing the optical element from being corotated by the mostly rotating abrasion tool during the processing.

In a particularly advantageous embodiment of the invention, it can be provided that the pressure piece has on its side facing the optical element a number of separate bearing elements that are provided for coming into contact with the optical element. Such bearing elements distributed over the pressure piece constitute an embodiment of the adaptation of the pressure piece to the pressure distribution to be expected inside the optical element during the processing of the latter that is particularly easy to implement, since the introduction of force from the pressure piece into the optical element can be controlled by the distribution of the bearing elements over the surface of the pressure piece.

A particularly simple mounting of the bearing elements on the pressure piece is provided when at least some of the bearing elements are of substantially round design. A further advantage of this embodiment consists in the fact that a particularly accurate force distribution is possible over the surface of the pressure piece with the aid of round bearing elements.

In a further refinement of the invention, it can be provided that the pressure piece has a cross section adapted to the force distribution to be expected inside the optical element during the processing of the optical element, the pressure piece having in those regions where a higher force is to be expected a greater thickness than in those regions where a lower force is to be expected. This embodiment, in which the stiffness of the pressure piece is transmitted to the optical element as a function of the thickness of said pressure piece constitutes a commercially acceptable alternative to the use of the abovedescribed bearing elements, although combinations of these two embodiments are also conceivable.

An embodiment of the force applying device that is very commercially acceptable results when the latter has a membrane acting on the pressure piece. The advantages achievable with this embodiment can be further enhanced when pneumatic pressure can be applied to the membrane.

Claim 14 specifies a method for the abrasive processing of an optical element in which the optical element is pressed against a rotating abrasion tool with the aid of an apparatus. Such a method can be used to produce optical elements such as lenses, having slight deformations and a very high accuracy.

Further advantageous refinements and developments of the invention emerge from the remaining subclaims. An exemplary embodiment of the invention is explained below in principle with the aid of the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a section through a holding apparatus according to the invention for an optical element that is being processed with an abrasion tool; and

FIG. 2 shows a plan view of the apparatus from FIG. 1.

DETAILED DESCRIPTION

FIG. 1 shows a section through a holding apparatus 1 for an optical element 2. In the present case, the optical element 2 is a lens, but it would likewise also be possible to hold other optical elements 2, such as, for example, mirrors or the like, in the holding apparatus 1. The size of the optical element 2 plays only a very subordinate role here. The holding apparatus 1 has a force applying device 3 that is provided for the purpose of pressing the optical element 2 against an abrasion tool 4, represented by a dashed and dotted line, during an abrasive processing of said optical element, and thus to apply the force required for the processing. The designation “abrasive processing” is understood in the present case as, for example, a polishing or grinding operation and so the abrasion tool 4 can be a grinding or polishing element that can be of known design, and is therefore not described in more detail below. The abrasion tool 4 should be rotated about its longitudinal axis in order to achieve a cutting speed.

The force applying device 3 has a feed bore 6 that is arranged in a basic body 5 of the holding apparatus 1 and is provided for applying a pneumatic pressure to a membrane 7 of the force applying device 3. The pneumatic pressure introduced via the feed bore 6 into the holding apparatus 1 and applied to the membrane 7 can be produced in a way known per se but not illustrated in the present case. The membrane 7 clamped between the basic body 5 and a supporting ring 8 arches, upon the application of pressure, in the direction of a movable pressure piece 9 that is in contact with the optical element 2 and is capable of pressing the latter against the abrasion tool 4 in the direction of the arrow “X”. During this movement, the pressure piece 9 is guided through the lateral supporting ring 8. Furthermore, the supporting ring 8 serves the purpose of supporting the optical element 2 at its periphery. In order to prevent damage to the optical element, the supporting ring 8 preferably consists of plastic, but it could also likewise consist of aluminum or another suitable metal.

In order in the case of the abrasive processing of the optical element 2 to produce the smallest possible deformation of the latter, as explained below with the aid of an exemplary embodiment the pressure piece 9 is adapted to a force distribution to be expected inside the optical element 2 during the processing of the optical element 2. In the exemplary embodiment illustrated, the pressure piece 9 has on its side facing the optical element 2, that is to say on its side averted from the membrane 7, a number of separate bearing elements 10 that are provided for the purpose of coming into contact with the optical element 2. As is to be seen in FIG. 1, the bearing elements 10 form that part of the pressure piece 9 that is in contact with the optical element 2. By contrast, the pressure piece 9 does not touch the optical element 2 in the interspaces between the bearing elements 10. The pressure piece 9 is provided with appropriate depressions 11 into which the bearing elements 10 are preferably bonded for the purpose of holding the bearing elements 10.

As FIG. 2 makes plain, the bearing elements 10 are of substantially round design, but annular bearing elements 10 or ones having another suitable shape would also be conceivable and, of course, bearing elements 10 having an annular, oval, round or some other shape could also be used with one and the same pressure piece. The bearing elements 10 preferably consist of an elastic material that prevents damage to the optical element 2 and simultaneously ensures that an undesired movement of the optical element 2 is prevented during rotation of the abrasion tool 4. The preferably elastic material of the bearing elements 10 can be, for example, rubber, or also a relatively soft plastic.

The distribution or arrangement of the bearing elements 10 over the surface of the pressure piece 9, as well as the shape and the size of the same is preferably set up via a calculation using a finite element method with the aid of which it is possible to determine those points or regions of the optical element 2 at which during the processing of the optical element 2 with the abrasion tool 4 a higher force occurs than in other regions of the optical element 2. Consequently, it is precisely the more highly loaded regions of the optical element 2 that are more strongly supported such that lesser deformations are to be expected there than in the case of customary processing. This leads finally to a uniform force distribution inside the optical element 2 during an abrasive processing of the latter such that only very slight deformations of the optical element 2 result. The bearing elements 10 can also exhibit different hardnesses for one and the same pressure piece 9 in order to achieve a better adaptation to the force distribution to be expected inside the optical element 2 during the processing thereof. Since finite elements methods are known per se, it is not necessary for the same to be examined in more detail here.

The distribution illustrated for the bearing elements 10 over the surface of the pressure piece 9 is to be considered as purely exemplary and suitable for a specific optical element 2, and it is advantageous with reference to a deformation of the optical element 2 that is as slight as possible during the abrasive processing of said element when a separate calculation of the required distribution of the bearing elements 10 is carried out for each geometrically different design of the optical element 2 to be processed. The pressure piece 9 can thereby have a larger number of bearing elements 10 in those regions where a higher force is to be expected than in those regions where a lower force is to be expected. If very similar results are returned in calculating the distribution of the bearing elements 10 for different optical elements 2, it is possible, of course, to design only one identical pressure piece 9 for these different optical elements 2.

As an alternative, or in addition to the embodiment illustrated, it would also be possible to adapt the cross section of the pressure piece 9 to the force distribution inside the optical element 2 to be expected during the processing of the optical element 2. The pressure piece 9 would thereby be provided in those regions where a higher force is to be expected with a greater thickness, that is to say a greater extent in the x-direction, than in those regions where a lower force is to be expected. In order to transmit the force transmitted to the pressure piece 9 by the force applying device 3 to the optical element 2 without producing impermissibly high deformations on said optical element, it would be advantageous in this case to adapt the pressure piece on its side facing the optical element 2 to the surface of the optical element 2, that is to say to provide the pressure piece 9 with a curvature corresponding to the curvature of the optical element 2. Damage to the optical element 2 could be prevented in this case were the pressure piece 9 provided on its side facing the optical element 2 with a corresponding, preferably elastic material preventing damage to the optical element 2 such as plastic or rubber. It is particularly expedient when, as is to be preferred, the pressure piece 9 consists of metal, preferably of steel or aluminum. It is also possible, however, to use glass or a plastic of suitable hardness for the pressure piece 9.

Instead of the abovedescribed application of pneumatic pressure to the membrane 7, it would also be possible to apply hydraulic pressure, for example, to said membrane, or it would also be possible in an embodiment not illustrated to dispense with the membrane 7 and to move the pressure piece 9 purely mechanically in the x-direction, for example by means of one or more spring elements. Also conceivable, moreover, would be to drive the pressure piece 9 by means of an electric motor or any other possibility with which the pressure piece 9 could be brought to press the optical element 2 against the abrasion tool 4.

In the case of one embodiment of the holding device 1 that is not illustrated, it would be possible to dispense with the force applying device 3 and to use the abrasion tool 4 to apply the force required for the processing. The pressure piece 9 could then be rigid and support the optical element 2 against the force applied by the abrasion tool 4.

It is possible with the aid of the holding apparatus 1 described herein to press the optical element 2 against the rotating abrasion tool 4 in a method for abrasive processing of said optical element. 

1. A holding apparatus for an optical element that holds the optical element during the abrasive processing thereof, wherein the optical element is in contact with a pressure piece that is adapted to a force distribution to be expected inside said optical element during processing of said optical element.
 2. The apparatus as claimed in claim 1, having a force applying device that is provided for the purpose of pressing the optical element against the abrasive tool during the abrasive processing thereof, wherein the force applying device acts on said pressure piece, which can move in the direction of the abrasion tool.
 3. The apparatus as claimed in claim 1, wherein said pressure piece has on its side facing the optical element a material that prevents damage to the optical element by said pressure piece.
 4. The apparatus as claimed in claim 1, wherein said pressure piece has on its side facing the optical element a number of separate bearing elements that are provided for coming into contact with the optical element.
 5. The apparatus -as claimed in claim 4, wherein at least some of the bearing elements are of substantially round design.
 6. The apparatus as claimed in claim 4, wherein at least some of the bearing elements are of substantially annular design.
 7. The apparatus as claimed in claim 1, wherein said pressure piece has a cross section adapted to the force distribution to be expected inside the optical element during processing of the optical element, said pressure piece having in those regions where a higher force is to be expected a greater thickness than in those regions where a lower force is to be expected.
 8. The apparatus as claimed in claim 4, wherein said pressure piece has a larger number of bearing elements in those regions where a higher force is to be expected than in those regions where a lower force is to be expected.
 9. The apparatus as claimed in claim 7, wherein said pressure piece is adapted to the surface of the optical element on its side facing the optical element.
 10. The apparatus as claimed in claim 2, wherein said force applying device has a membrane acting on said pressure piece.
 11. The apparatus as claimed in claim 10, wherein pneumatic pressure can be applied to the membrane.
 12. The apparatus as claimed in claim 1, wherein said pressure piece consists of metal, glass or plastic.
 13. The apparatus as claimed in claim 1, wherein a supporting ring is provided on the side facing the optical element for the purpose of supporting the optical element at its periphery.
 14. The apparatus as claimed in claim 13, wherein said supporting ring consists of plastic or metal.
 15. A method for the abrasive processing of an optical element, wherein the optical element is pressed against a rotating abrasion tool by means of a holding apparatus as claimed in claim
 1. 